This invention relates to mechanical seals for use with rotating equipment such as pumps, mixers, agitators and the like. The invention is particularly well suited for use with rotating equipment used in the moving, agitating or stirring of fluids containing abrasive particles either in solution or in suspension (slurries). In most commonly available rotating equipment a mechanical seal is positioned between a stationary element (such as a pump casing), and a rotating element (such as a rotating shaft) so as to prevent leakage from the rotating equipment of the fluids being moved or mixed. Most seals utilize two distinct flat surfaces or "faces" which are urged together with sufficient force to prevent passage of the contained fluid, yet which can rotate relative to each other.
Slurry mechanical seals are subject to a considerable amount of torsional load (both constant and intermittent) due to the combination of the compressive force urging the seal faces together and the rotation of the faces relative to each other. The torsional load varies with the amount of compressive force, speed of rotation, degree of face lubrication, and varying forces within the fluid containing vessel. Shock torsional loadings on the seal faces caused by changing conditions, including changing hydraulic forces with the fluid containing vessel can result in `stalling` (prevention of rotary motion) of the rotating element, possibly resulting in damage to the drive mechanism. To reduce the possibility of damage from `stalling` or an intermittent `slip-stick` condition, the preferred embodiment of the mechanical seal which is the subject of this invention incorporates a system of elastomeric drive lugs in combination with an annular cone spring to accommodate shock torsional loadings.
Slurry mechanical seals are subject to considerable abrasive forces due to their exposure to the abrasive fluids in which they operate, which leads to the wearing of various components of the seal to conditions where the seal needs to be replaced. Abrasive particles can cause deterioration of the seal faces, resulting in leakage of the contained fluid, and necessitating relatively frequent replacement of the damaged faces. To replace a traditional mechanical seal the rotating equipment has to be disconnected from the driving motors and skilled mechanics must dismantle the pump, mixer or agitator, to remove the damaged or worn seal and replace it. Such a seal change may cause an interruption of the process and loss of valuable production time with a relatively high labor and replacement cost. To eliminate such problems mechanical seals were developed having both seal faces separable into two haves ("split"), such that the seal faces could be placed around the shaft of the rotating equipment without removing the equipment from drive mechanism. U.S. Pat. No. 4,576,384 describes a split seal with stationary and rotating wear faces. However, many split seals have a plurality of small parts and fine clearances. When used in an abrasive liquid such seals are subject to excessive wear. Additionally, abrasive material settles in the fine clearances and causes such seals to bind. These difficulties often require a premature change of the seal assembly and a loss of valuable production time. Furthermore, a plurality of small parts and fine clearances makes many such seals difficult to assemble and therefore prone to leaking, due to the possibility of misalignment. The mechanical seal which is the subject of this invention incorporates fractured seal faces attached to elastomeric material which facilitates easy replacement and alignment of the seal faces.
Most mechanical seals utilize a spring or springs to thrust the wear faces of the seal together to prevent leakage. The extent to which the spring is deflected determines the compressive force on the faces. Too little compression may result in leakage across the wear faces; too much compressive may cause "slip-stick" condition, and result in premature wear of the faces.